The Earth’s Crust

1. The Earth’s Crust

2. Plates • The earth’s crust is broken into several large slabs of rock called plates • Each plate floats on a partially melted layer in the upper mantle • The plates carry the earth’s oceans and continents

4. Movement • Over time the plates move • Millions of years ago the continents were joined in one supercontinent called Pangea • Over millions of years the plates have drifted to where they are currently • Continental drift – the theory that the continents were once joined and then slowly drifted apart • The movement of plates is very small and cannot be felt, only about 4 inches a year

6. Movement • As the plates move they are bound to crash into each other, pull apart, grind together, or slide past each other • Plate tectonics – the activities of continental drift that create many of the earth’s physical features • The shifting of plates means that the earth could look very different millions of years from now

7. Colliding and Spreading Plates • Mountains are formed when two plates collide • Subduction – occurs when a heavier sea plate dives beneath the lighter continental plate • When the sea plate plunges down it becomes molten material and eventually bursts out as magma forming volcanic mountains

8. Colliding and Spreading Plates • Spreading – when sea plates pull apart. The resulting rift allows magma to come up and harden to build underwater mountains or volcanoes • Fault – when two plates grind or slide past each other creating a crack in the earth’s crust